Well, what we really need is a sane way of forbidding drugs when we don't want most dwarves to use them, where unforbidding them doesn't just result in a flood of dwarves all trying to take the same pills.
Aside from rolling it in with the priorities list and expanding alert status (possibly, just making alert status some sort of easy-toggle set of job priorities list), which I think should be fairly decent, as it means that, while it may be a little trouble to give a "just this once" order, it would have the benefit of streamlining the interface. Being as a glut of overlapping interfaces is one of those problems DF has, trying to keep the interface streamlined when adding new things should help.
The other option, if you really must add in a new menu, would be, perhaps, a "Pharmacy" menu, where Dr McDoctor could perscribe potions and pills and tinctures, along with an order for when to use them. (This would potentially make the dwarf put in charge of the pharmacy the equivalent of an arsenal dwarf, as well.) That way, "when depressed, take two Happy Juice, and call me in the morning" could be a standing order. Something like "poison your blades" or "drink a Maddened Boar" would still require alert status, though.
This latter, however, would have the negative effect of not streamlining how you see what standing orders are in effect over your individual dwarves - you would need to look through multiple menus (Standing Orders, Job Priorities, Burrows, Military Screen, and Pharmacy Menu) to see every order/list of orders you've given to a dwarf. There's an advantage to making just one screen, even if it's a clunky screen to navigate because of it, have all the information on a dwarf that you need.
It's why Dwarf Therapist is of such benefit - it reformats the data you need to play the game to be easier to read.